The present invention relates generally to vapor sensors, and more particularly to optical sensors for sensing alkane gases.
The development of devices for detecting toxic gases is currently an active area of research. It is highly desirable that such detecting devices be reversible, i.e., that the devices return to a baseline when the toxic gas is removed in order that the device can be reused. One such device is described in U. S. patent application Ser. No. 462,493, filed Jan. 31, 1983, entitled "REVERSIBLE OPTICAL WAVEGUIDE VAPOR SENSOR", now U.S. Pat. No. 4,513,087. This device is specifically designed to detect toxic gases such as ammonia and hydrazine. The device includes an optical waveguide, a dye film coated on the waveguide, and means for detecting a change in the optical transmittance of the waveguide. The dye film has the property of changing from its normal color to another color when it is exposed to the chemical to be detected, and then returning to its original color when the chemical is removed. The optical transmittance of the waveguide accordingly varies with the color change of the dye film coating, thereby providing an indicator which is sensitive to the presence of the chemical to be detected.
However, the above-described device is not capable of detecting explosive vapors, such as the alkane gases, because no known dyes are available which will operate to change the transmittance property of a waveguide in the presence of alkane gas. The alkane gases, such as methane, ethane, propane, and butane, are inert molecules (non-polar), and do not form an attraction to any known dye coating.
However, with the widespread use of natural gas for industrial and home heating fuel, a reliable, low cost, portable, and a sensitive leak detection system is desired. Such leak detection systems would be installed in inaccessible areas such as underground fuel lines, home and industrial furnaces, and other stations where potential natural gas leaks would provide the potential for explosions. Additionally, there is also a need for sensitive, portable, low cost, hydrocarbon detectors in the petroleum industry, where the detection of natural gas in the oceans is used to indicate the presence of oil deposits. Additionally, this type of alkanes detector is also needed in mining applications.